1. Field of the Invention
This invention relates generally to printers and particularly to an ink ribbon feeding mechanism in a printer. More specifically, the present invention relates to an ink ribbon cassette which is provided with an ink ribbon feeding mechanism and which can be detachably mounted in a printer.
2. Description of the Prior Art
An ink ribbon cassette housing therein ink ribbon for use in a printer as detachably mounted therein is well known in the art. Such an ink ribbon cassette is generally provided with a supply spool around which ink ribbon to be used for printing is wound and a take-up spool to which the ink ribbon is wound after having been used for printing. Thus, the ink ribbon is gradually fed from the supply spool to the take-up spool by an ink ribbon feeding mechanism. Such a typical prior art ink ribbon feeding mechanism is shown in FIGS. 1 and 2. As shown, upstream of a take-up spool 1 with respect to the feeding direction of ink ribbon 6 is disposed a capstan roller 2. Also disposed is a pinch roller 4 pressed against the capstan roller 2 by means of a spring 3. In the illustrated structure, the capstan roller 2 is rotatably supported by a stationary holder 2a which is fixedly mounted on an ink ribbon cassette 5, and the pinch roller 4 is rotatably supported by a movable holder 4a which is movably mounted on the cassette 5 in rolling contact under pressure with the capstan roller 2. The take-up spool 1 is also rotatably mounted on the cassette 5.
Typically, when the cassette 5 is set in position in a printer, the capstan roller 2 is operatively coupled to a driving shaft provided in the printer. Thus, as printing proceeds, the driving shaft rotates thereby causing the capstan roller 2 to rotate counterclockwise as indicated by the arrow so that the ink ribbon 6 pinched between the rollers 2 and 4 is fed toward the take-up spool 1 to be wound therearound. Although not shown specifically in FIG. 1, the printer is also provided with a mechanism for rotating the take-up spool 1 in association with the rotation of the capstan roller 2. Such a mechanism typically includes an endless belt extended between the capstan roller 2 and the take-up spool 1. Thus, the ink ribbon 6 can be immediately wound around the take-up spool 1 as fed by the rollers 2 and 4 without producing a slack.
As shown in FIG. 2, the cassette 5 includes a top cover 7 which is pivotally supported at a pivot 8 at each side, and, thus, the top cover 7 can be pivotally moved to open or close the cassette 5.
As described above, the capstan roller 2 is provided rotatably but fixed in position inside of the cassette 5; on the other hand, the pinch roller 4 is rotatably supported by the movable holder 4a which is movable with respect to the cassette 5 and normally biased toward the capstan roller 2 under the pressure of the spring 3. For this purpose, the movable holder 4a is typically so structured to be slidable on the bottom surface of the cassette 5. With this structure, when the cassette 5 is to be assembled or the ribbon 6 is to be replaced with new one, the pinch roller 4 must be moved away from the capstan roller 2 against the force of the spring 3 so as to place the ink ribbon 6 in position or to remove it therefrom. In this connection, it is often required to keep the pinch roller 4 away from the capstan roller 2 so as to facilitate positioning or removal of the ink ribbon 6, and, in this case, the operator's one hand must be used exclusively for this purpose. This is however disadvantageous because the operator must carry out the remaining operation with a single hand. For example, the ink ribbon 6 is relatively thin, typically 10 microns in thickness, and it is not easy to place such a thin ink ribbon around a guide 9 to the take-up spool 1 through the rollers 2 and 4 with one hand. In the case of an awkward operator, the ink ribbon 6 could be damaged.